Chromatic dispersion compensation system and method

ABSTRACT

Dispersion compensation is provided in an optical transmission system. An optical line couples first and second transceivers, and a plurality of amplifiers coupled to the optical line are spaced throughout the optical line with variable span distances. A plurality of dispersion compensation modules include a coarse granularity fiber, a connector, and a fine granularity fiber. A memory is associated with the dispersion compensators to provide information related to the value of the dispersion compensation.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/179,134, filed Jul. 11, 2005, which is a continuation of U.S. patentapplication Ser. No. 10/147,397, filed May 15, 2002 now, U.S. Pat. No.6,965,738, issued Nov. 15, 2005, which claims benefit under 35 U.S.C.§119(e) of U.S. Provisional Application No. 60/372,845, filed Apr. 16,2002, each of which is hereby incorporated by reference in its entirety.This application is related by subject matter to U.S. patent applicationSer. No. 10/454,812, filed Jun. 3, 2003 and to U.S. patent applicationSer. No. 11/515,480, filed Aug. 31, 2006.

TECHNICAL FIELD

This invention relates to a dispersion compensation system and moreparticularly to a chromatic dispersion compensation system for use inoptical transmission systems.

BACKGROUND

The transmission, routing and dissemination of information has occurredover computer networks for many years via standard electroniccommunication lines. These communication lines are effective, but placelimits on the amount of information being transmitted and the speed ofthe transmission. With the advent of light-wave technology, a largeamount of information is capable of being transmitted, routed anddisseminated across great distances at a high transmission rate overfiber optic communication lines.

When information is transmitted over fiber optic communication lines,impairments to the pulse of light carrying the information can occurincluding pulse broadening (dispersion) and attenuation (energy loss).As an optical signal is transmitted over the fiber optic communicationline, the optical signal is transmitted at various frequencies for eachcomponent of the optical signal. The high frequency components movethrough the fiber optic material at different speeds then compared tothe low frequency components. Thus, the time between the fastercomponents and the slower components increase as the optical signal istransmitted over the fiber optic communication line. When this occurs,the pulse broadens to the point where it interferes with the neighboringpulses; this is known as chromatic dispersion. Chromatic dispersioncompensation corrects this pulse broadening. Various chromaticdispersion compensation apparatus and methods are available. In U.S.Pat. No. 6,259,845 entitled “Dispersion Compensating Element Having anAdjustable Dispersion” issued to Harshad P. Sardesai, a variabledispersion compensation module is disclosed. In the Sardesai patent, adispersion compensation module including segments of optical fiber ofvarying lengths, some of which have a positive dispersion while othershave a negative dispersion is disclosed. Selected optical fiber segmentsare coupled to one another to provide a desired net dispersion to offsetthe dispersion associated with the fiber optic communication line. TheSardesai patent allows for this variable dispersion compensation modelrather than provide a unique segment of dispersion compensation fiberfor each span. The Sardesai dispersion compensation module functions byinterconnecting the various length of various dispersion per kilometerfibers so that the resulting total dispersion equals the dispersion ofthe fiber optic communication line span. The Sardesai dispersioncompensation module, however, has a high cost in that multipledispersion compensation fibers enclosed within the Sardesai compensationmodule may remain unused and are therefore wasted when implemented inthe field. Further, the Sardesai dispersion compensation module requiresexcessive interconnectivity between the various dispersion compensationfibers, allowing for a greater connection loss to be experienced.

U.S. Pat. No. 6,275,315 entitled “Apparatus for Compensating forDispersion of Optical Fiber in an Optical Line” issued to Park, et al.discloses a dispersion compensation method in which dispersioncompensation fiber is used in conjunction with a variable dispersionmodule. In the Park patent, the variable dispersion compensation moduleis a dispersion compensation filter such as a reflective etalon filter.The etalon filter is a tunable filter and thus allows for variabledispersion compensation.

The primary focus of the fiber optic industry to correct chromaticdispersion has followed one of two paths. The first path was for the useof variable dispersion compensation modules as has been disclosed in theabove referenced patent/patent applications. A second path is tomanufacture dispersion compensation fibers in varying lengths to correctfor dispersion compensation. Each varying length of the dispersioncompensation fiber must be inventoried requiring a vast amount of assetsto be tied up in inventory which is infrequently implemented. Therefore,any advancement in the ability to reduce the number of interconnectivitypoints between the dispersion compensating fibers and to reduce the costincurred with the highly technical variable dispersion compensators andthe high cost of inventory would be greatly appreciated.

SUMMARY

A dispersion compensation system and method for use in an opticaltransmission system to compensate for signal distortion of an opticalsignal is provided. The dispersion compensation system includes a firstand second transceivers for generating and receiving the optical signalrespectively. An optical line couples the first transceiver to thesecond transceiver. A plurality of amplifiers are coupled to the opticalline, spaced periodically throughout the optical line forming spandistances, wherein the amplifiers amplify the optical signal and whereinthe span distances are variable. A plurality of dispersion compensationmodules are coupled to the plurality of amplifiers wherein thedispersion compensation models include a coarse granularity modulehaving a resolution of at least 5 kilometers coupled to a connector. Theconnector is also coupled to a fine granularity module having aresolution of one kilometer. The coarse and fine granularity modules areconnected through a single connector. The coarse granularity modules andthe fine granularity modules correct the dispersion of the opticalsignal accumulated in the variable span distance.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the invention can be obtained from thefollowing detailed description of one exemplary embodiment as consideredin conjunction with the following drawings in which:

FIG. 1 is a block diagram depicting an optical transmission systemaccording to the present invention;

FIGS. 2 a, 2 b, 2 c, 2 d are graphical representations of an eye diagramof the optical signal;

FIG. 3 is a block diagram depicting a dispersion compensation moduleaccording to the present invention;

FIG. 4 a is a block diagram depicting exemplary fiber combinationsaccording to the present invention;

FIG. 4 b is a block diagram depicting exemplary fiber combinationsaccording to the present invention;

FIG. 4 c is a block diagram depicting exemplary fiber combinationsaccording to the present invention;

FIG. 5 is a flow chart of the dispersion compensation method accordingto the present invention; and

FIG. 6 is a flow chart depicting the inventory reduction of dispersioncompensation fibers method according to the present invention.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

In the descriptions that follow, like parts are marked throughout thespecification and drawings with the same numerals, respectively. Thedrawing figures are not necessarily drawn to scale and certain figuresmay be shown in exaggerated or generalized form in the interest ofclarity and conciseness.

FIG. 1 depicts an optical transmission system according to the presentinvention. An optical transmission system 100 is shown including atransmitting terminal 102 and a receiving terminal 104. For illustrativepurposes only, the optical transmission system 100 is shown in aunidirectional manner. However, as is known to those skilled in the art,the optical transmission system 100 can function in a bi-directionalmanner without detracting from the spirit of the invention. Thetransmitting terminal 102 and the receiving terminal 104 are connectedthrough optical line 106. An optical signal 108 is transmitted over theoptical line 106. Spaced periodically throughout the opticaltransmission system 100 are in-line amplifiers 110. The in-lineamplifiers 110 boost the optical signal 108 as it is transmitted overthe optical line 106. As the optical signal 108 is transmitted over theoptical line 106, the optical signal 108 begins to experience chromaticdispersion. Chromatic dispersion is the broadening of the optical pulseover the various frequencies of the components of the optical signal108. High frequency components of the optical signal move through theoptical line 106 at a different speed when compared to the low frequencycomponents of the optical signal 108. The longer wave-length componentsmove at a slower rate than the shorter wave-length components of theoptical signal 108. Therefore, the optical signal 108 pulse broadensover time as the optical signal is transmitted throughout the opticalline 106. Chromatic dispersion compensation is necessary to correct forthis pulse broadening impairment.

A controller 115 is resident in each in-line amplifier 110 and connectsthe in-line amplifiers 110(a-e) to the optical supervisory channel 114through transmission lines 118(a-e). The controllers 115(a-e) receiveand transmit control data for the in-line amplifiers 110(a-e). Thecontroller in one embodiment includes a processor, a mass storagedevice, a network connection and a memory (all not shown). However, awide range of controllers are implementable without detracting from thespirit of the invention.

A dispersion compensation module 112 is coupled to the in-lineamplifiers 110 such that the optical signal 108 flows through thedispersion compensation module 112 as the optical signal 108 istransmitted along the optical line 106. The dispersion compensationmodules 112(a-e) are electronically coupled to the controllers 115(a-e)and receive control data from the optical supervisory channel 114through transmission lines 118(a-e) via the controllers 115(a-e). As canbe seen, dispersion compensation modules 112(a-e) are located at eachin-line amplifier 110(a-e) location in the optical transmission system100. However, the quantity of dispersion compensation modules may bevaried, including locating dispersion compensation modules at everyother in-line amplifier or by selecting a fixed number of dispersioncompensation modules and distributing those dispersion compensationmodules at fixed intervals through the optical transmission system,without detracting from the spirit of the invention. Thus, in oneembodiment, a dispersion compensation module 112 a is shown co-locatedwith in-line amplifier 110 a within the optical transmission system 100.The distance between the transmitting terminal 102 and the first in-lineamplifier 110 a and the distances between a first in-line amplifiers 110and an adjacent amplifier 110 may vary according to the physical layoutof the optical transmission system 100. Thus, the frequency of thein-line amplifiers 110 within the optical transmission system 100 mayvary depending upon the type of fiber used in the optical line 106 anddepending upon the physical terrain that the optical transmission system100 must span. The distances between the transmitting terminal 102 andthe first in-line amplifier 110 a, the distances between adjacentin-line amplifiers 110 and the distances between the receiving terminal104 and the last in-line amplifier 110 e may vary and each distancedefined is a spanned distance.

Referring now to FIG. 2, graphical representations of the eye diagram ofthe optical signal are shown. As the optical signal 108 is transmittedover a standard optical system, a optimal pulse shape is initiallytransmitted. The optimal pulse shape can be seen in FIG. 2 a. Theoptimal pulse shape forms an “eye” and represents the minimum amount ofchromatic dispersion of the optical signal 108 pulse. As the opticalsignal 108 is transmitted over the optical transmission network 100, thepulse begins to broaden as is shown in FIGS. 2 b and 2 c. As the pulsebroadens, the distinctions between separate optical signal 108 pulsesbecome less discernable. As the optical signal 108 is transmittedfurther along the optical line 106, the optical signal 108 continues tobroaden as is shown in FIG. 2 d. Thus, as the optical signal 108 istransmitted over the optical line 106, the optical signal 108 broadensto a point in which the information being transmitted over the opticalsignal 108 is no longer discernable. Thus, the optical signal 108requires a chromatic dispersion correction to maintain an adequate “eye”or pulse shape.

Referring now to FIG. 3, the dispersion compensation module according tothe present invention is shown. Current dispersion compensationmethodologies which incorporate dispersion compensation fibers can beclassified in two groups. The first methodology includes the use of adispersion compensation fiber in combination with a tunable dispersioncompensation filter. The tunable compensation filter allows for the finetuning of the dispersion compensation module to be accomplished when theexact amount of dispersion over a span is not known. Thus, when in thefield, the installer can adjust through the interconnection of multipledispersion compensation fibers within the tunable dispersioncompensation module to accomplish the level of dispersion compensationnecessary to offset the chromatic dispersion present in the currentspan. Examples of this methodology include U.S. Pat. No. 6,259,845 andU.S. Patent Application No. US2001/0009468 discussed herein. A secondmethodology requires that the exact dispersion amount of the span becalculated and then a single piece dispersion compensation fiber thatexactly matches this specific dispersion amount be manufactured orobtained from a current inventory and installed to offset the chromaticdispersion of the span. A third methodology now exists and is discussedherein.

The dispersion compensation module 112 according to the presentinvention is comprised of a coarse granularity fiber 300 and a finegranularity fiber 302 interconnected with connector 304. The coarsegranularity fiber 300 compensates for the dispersion slope of the fiberand includes multiple dispersion compensation devices such as dispersioncompensating fiber, higher order mode devices and chirped fiber bragggratings. The fine granularity fiber 302 includes dispersioncompensating fiber, higher order mode devices and chirped fiber bragggratings but further includes the use of a standard single mode fiber(SSMF). The connector 304 is of the type commonly known to those skilledin the art for the connection of dispersion compensation fibers.

A memory 306 is physically coupled to the coarse granularity fiber 300and is coupled to the controller 115 through communication line 312. Asecond memory 308 is physically coupled to the fine granularity fiber302 and is coupled to the controller 115 through communication line 314.The memories 306 and 308, in one embodiment, are programmable read-onlymemories, preferably electronically erasable programmable read-onlymemories. However, multiple memory systems are implementable withoutdetracting from the spirit of the invention. Unique identifiers arestored in the memories 306 and 308 and upon a query from the controller115, the unique identifiers are transmitted to the controller 115 forretransmission across the optical supervisory channel 114. Further, theunique identifiers are ascertainable through direct electricalconnection to the in-line amplifier 110 as would occur by maintenancepersonnel in the field. The unique identifiers allow the maintenancepersonnel to identify the specific coarse and fine granularity fibers300 and 302 installed in the dispersion compensation module 112. Uponvisual inspection, the resolution of the coarse and fine granularityfibers 300 and 302 is difficult to ascertain. However, if eachindividual fiber or each resolution or length of the coarse and finegranularity fibers 300 and 302 are assigned unique identifiers, themaintenance personnel only need cross reference the unique identifierwith a master list to distinctly identify the resolution of the coarseand fine granularity fibers 300 and 302. The coarse and fine granularityfibers 300 and 302 are manufactured at specific lengths, theninventoried such that through the use of only one coarse granularityfiber, one fine granularity fiber and one connector the dispersionaccumulated in any standard span, which typically has a range of lessthan 100 kilometers, can be compensated. In one embodiment of thepresent invention, the coarse granularity fibers 300 are manufacturedand inventoried at lengths which correspond to the accumulateddispersion in the optical network 100 for lengths of 10 kilometers, 20kilometers, 30 kilometers, 40 kilometers, 50 kilometers, 60 kilometers,70 kilometers, 80 kilometers, 90 and 100 kilometers. The finegranularity fibers 300 are manufactured and inventoried at lengths whichcorrespond to the accumulated dispersion in the optical network 100 forlengths of 1 kilometer, 2 kilometers, 3 kilometers, 4 kilometers, 5kilometers, 6 kilometers, 7 kilometers, 8 kilometers and 9 kilometers.Therefore for any span under 109 kilometers, the dispersion compensationmodule according to one embodiment of the present invention isimplemented with only one coarse granularity fiber 300, one finegranularity fiber 302 and one connector 304. In another embodiment ofthe present invention, the coarse granularity fibers 300 aremanufactured and inventoried at lengths which correspond to theaccumulated dispersions in the optical network 100 for lengths of 5kilometers, 10 kilometers, 15 kilometers, 20 kilometers, 25 kilometers,30 kilometers, 35 kilometers, 40 kilometers, 45 kilometers, 50kilometers, 55 kilometers, 60 kilometers, 65 kilometers, 70 kilometers,75 kilometers, 80 kilometers, 85 kilometers, 90 kilometers, 95kilometers, 100 kilometers. The fine granulated fibers 300 aremanufactured and inventoried at lengths which correspond to theaccumulated dispersion in the optical network for lengths of −5kilometer, −4 kilometer, −3 kilometer, −2 kilometer, −1 kilometer, 1kilometer, 2 kilometers, 3 kilometers, 4 kilometers, 5 kilometers.Therefore, for any span under 105 kilometers, the dispersioncompensation model according to one embodiment of the present inventionis implemented with only coarse granularity fiber 300, one finegranularity fiber 302 and one connector 304. The benefits of suchsystems are the reduction of manufacturing costs, the reduction ofinventory costs and the reduction of time necessary to identify andinstall the dispersion compensation module 112.

In one prior art system in which a single dispersion compensation fiberis used to offset the chromatic dispersion associated with any variablespan under 109 kilometers, 109 different dispersion compensation fiberlengths would be necessary to offset the chromatic dispersionaccumulated in various lengths varying from 1 to 109 kilometers.According to the present invention, only 19 various dispersioncompensation fiber lengths would be necessary to be manufactured andinventoried. In another prior system, a tunable dispersion compensationmodule is attached to varying lengths of dispersion compensation fiber.However, the cost of the tunable dispersion compensation modules greatlyexceed the cost of the dispersion compensation fiber itself and atunable dispersion compensation module is necessary for each span.Further, the tunable dispersion compensation modules require multipleconnections between various lengths of dispersion compensation fiberswithin the tunable dispersion module and therefore incur a greateramount of loss due to each of these multiple connections. As can beseen, the present invention provides a simplified and cost effectivemethod of preparing a dispersion compensation module 112 as shown.

The dispersion compensation module 112 may be assembled in the field ifthe installer carries at least one each of the various lengths of thedispersion compensation fiber according to the present invention.Alternatively, the dispersion compensation module 112 may be assembledat the plant if the chromatic dispersion of the specific span is known.The dispersion compensation module 112 is then delivered and installedin the optical network by a field technician.

Referring now to FIGS. 4 a, 4 b and 4 c, exemplary block diagrams areprovided showing the various coarse and fine granularity fibersinterconnected. FIGS. 4 a through 4 c demonstrate various exemplaryembodiments of the dispersion compensation module. In FIG. 4 a, adispersion compensation module 112 is shown with a coarse granularityfiber 402 equivalent to 60 kilometers of accumulated dispersionconnected through connector 404 to a fine granularity fiber 406equivalent to the dispersion necessary for the accumulation of 2kilometers of dispersion. Therefore, through the use of the singlecoarse granularity fiber 402, the connector 404, and the finegranularity fiber 406 the total dispersion accumulated in 62 kilometersof the optical line 106 can be compensated. In FIG. 4 b, anotherexemplary embodiment is shown with the coarse granularity fiber 410equivalent to 40 kilometers of accumulated dispersion, connected throughconnector 404 with the fine granularity fiber 412 equivalent to 6kilometers of accumulated dispersion. Therefore, in this example, thedispersion associated with 46 kilometers has been offset through the useof the single coarse granularity fiber 410, fine granularity fiber 412and a connector 404. In FIG. 4 c, an alternative embodiment is shown.The coarse granularity fiber 416 is equivalent to the accumulateddispersion of 80 kilometers. The coarse granularity fiber 416 isconnected through connector 404 to a fine granularity fiber 418 of anaccumulated −2 kilometers. The −2 kilometer fine granularity fiber 418is typically a standard single mode fiber (SSMF). The fine granularityfiber 418 is used to compensate for the over compensation of the coarsegranularity fiber 416. Therefore, in this example, the total distance tobe compensated is 78 kilometers. To accomplish this, the 80 kilometercoarse granularity fiber 416 was coupled to a −2 kilometer finegranularity fiber 418. The benefits of this compensation for overcompensation of the coarse granularity fiber include: lower connectionlosses due to the connection of the SSMF to the coarse granularity fiber416 where the large connector losses are experienced between theconnection of two dispersion compensation fibers; a lower power loss isexperienced as a signal flows through the SSMF as compared to dispersioncompensation fiber; and the SSMF is a lower cost than the standarddispersion compensation fiber. Other fiber types such as non-zerodispersion shifted fiber and silica-core fiber may be implemented as thenegative fine granularity fiber without detracting from the spirit ofthe invention.

The dispersion compensation module 112 may include one device includingthe coarse granularity fiber and the fine granularity fiber, twodifferent sub-modules, one for the coarse granularity fiber and one forthe fine granularity fiber, or the fine granularity fiber may beintegrated into the coarse granularity fiber through connectors orsplices at manufacture. A wide range of connection possibilities existwithout detracting from the spirit of the invention.

FIG. 5 is a flow diagram of the dispersion compensation method accordingto the present invention. The process begins with start 500. Next, instep 502, the physical optical network path is identified. Thedevelopers of the optical network system identify the route in which theoptical network path will take over the physical terrain. Next, thelocations for the in-line amplifiers 110 are identified in step 504. Thelocation of these in-line amplifiers 110 depend upon the physicalterrain and the characteristics of the optical network. Next, in step506, the various distances between the in-line amplifiers 110, thedistance between the transmitting terminal 102 and the first inlineamplifier 110 a, and the distance between the last in-line amplifier 110e and the receiving terminal 104 are identified. As these distancesvary, the determination of the specific span distance for each span isnecessary to determine the accumulated dispersion over that span. Next,in step 508, the specific fiber type which will be used in the opticalnetwork is identified. Once this optical fiber type has been identified,the specific characteristics of this fiber are measured or obtained andwill be used to determine the amount of dispersion per kilometer of theoptical network. The calculation to determine the dispersion for eachspan in the optical network is accomplished in step 510. This dispersioncalculation depends on the specific span distances and the fiber typeand characteristics of the fiber selected. In an alternative embodiment,the measurement equipment will be taken out into the field to directlymeasure the dispersion amount of the particular deployed span. In thisembodiment, the accuracy of the dispersion is higher, as dispersion evenin the same fiber type might differ among different production batchesand the product of span length and average dispersion might give a lessaccurate result. Once the calculated accumulated dispersion for eachspan is determined, the coarse granularity fiber type is identified instep 512. The fine granularity fiber type is identified next in step514. The fiber types are selected based upon the characteristics of theoptical network fiber and are selected based upon the dispersioncalculations for each span. Next, in step 516, the coarse granularityfiber variable distances are determined In one embodiment, the coarsegranularity fiber variable distances are based upon 10 kilometergroupings. Therefore, the coarse granularity fiber variable distancesare 10 kilometers, 20 kilometers, 30 kilometers, 40 kilometers, etc. Thefine granularity fiber variable distances are identified in step 518.These fiber variable distances depend upon the total dispersion amountexperienced over the optical network and may depend upon the currentmanufacturing or inventory of specific variable distances. The variabledistances are determined such that one coarse granularity fiber and onefine granularity fiber are coupled to properly compensate for theaccumulated dispersion of any span distance in the optical network, thusreducing inventory and cost levels. Next, in step 520, the fine andcoarse granularity fibers are intercoupled to form a dispersioncompensation module 112. The dispersion compensation module may beformed in the field, interconnected at a assembly facility, or may beconnected at manufacturer if the manufacturer has access to the specificvariable distances. Finally, in step 522, the dispersion compensationmodule is coupled to the optical network to compensation for thechromatic dispersion accumulated in each span. The process ends withstep 524.

Referring now to FIG. 6, a method of inventory reduction of dispersioncompensation fibers is shown. The process begins with start 600. Next,in step 602, the required dispersion compensation accuracy is determinedon a per span basis based upon transmission system modeling. Next, instep 604, the lengths of the fine granularity compensation fibers aredetermined based upon the required compensation accuracy per span asdetermined in step 602. Next, in step 606, the lengths of the coarsegranularity fibers are determined based upon the maximum length of thefine granularity fibers and the range of dispersion that needs to becompensated. For the lowest overall number of different fiber modules,the number of coarse and fine granularity fibers should be approximatelyequal. The necessary lengths are determined such that only one coarseand only one fine granularity fiber can be coupled to compensate anystandard span distance. In one embodiment, the standard span distance isless than 109 kilometers. In another embodiment, the necessary lengthsof the coarse granularity fibers are based upon 10 kilometer incrementsand the fine granularity fibers are based upon 1 kilometer increments.In another embodiment, the fine granularity fiber compensate from a −9kilometers to a +9 kilometers. Next, in step 608, the optical networkprovider stocks only the necessary lengths of the coarse and finegranularity fibers. Thus, the intermittent lengths are not manufacturedor inventoried and thus the inventory is reduced thus lowering costs ofmanufacture and storage. In step 609 the unique identifiers for thecoarse and fine granularity fibers 300 and 302 are determined A uniqueidentifier is assigned to each individual fiber or a unique identifieris assigned to a specific length or resolution of the coarse and finegranularity fibers 300 and 302. The unique identifier is stored in amemory device 306 and 308 and is physically attached to the individualfibers. The manufactured and stored coarse and fine granularity fibers300 and 302 can be electronically polled and an automatic inventorylisting determined The process ends with step 610.

The foregoing disclosure and description of the invention areillustrative and explanatory thereof of various changes to the size,shape, materials, components and order may be made without departingfrom the spirit of the invention.

1. A method of stocking an inventory of dispersion compensation fibersfor use in an optical transmission system, the method comprising:determining a set of coarse granularity fiber lengths and a set of finegranularity fiber lengths, wherein combinations of one of the set ofcoarse granularity fiber lengths and one of the set of fine granularityfiber lengths span a range of possible dispersion values in the opticaltransmission system; stocking, in the inventory, one or more coarsegranularity fibers corresponding to each length in the set of coarsegranularity fiber lengths; and stocking, in the inventory, one or morefine granularity fibers corresponding to each length in the set of finegranularity fiber lengths; wherein each of the coarse granularity fibersand each of the fine granularity fibers is configured to provide a fixedamount of dispersion compensation.
 2. The method of claim 1, furthercomprising: stocking, in the inventory, a plurality of memory storagedevices, wherein at least one of the plurality of memory storage devicesis connectable to at least one of the coarse granularity fibers.
 3. Themethod of claim 2, further comprising: storing a unique identifierassociated with the at least one of the coarse granularity fibers in theat least one of the plurality of memory storage devices.
 4. The methodof claim 1, further comprising: stocking, in the inventory, a pluralityof memory storage devices, wherein at least one of the plurality ofmemory storage devices is connectable to at least one of the finegranularity fibers.
 5. The method of claim 4, further comprising:storing a unique identifier associated with the at least one of the finegranularity fibers in the at least one of the plurality of memorystorage devices.
 6. The method of claim 1, wherein the stocked one ormore coarse granularity fibers are configured to compensate for a fixedamount of dispersion in the optical transmission system corresponding tolengths in a range of about 10 km to about 100 km.
 7. The method ofclaim 1, wherein the stocked one or more fine granularity fibers areconfigured to compensate for a fixed amount of dispersion in the opticaltransmission system corresponding to lengths in a range of about 1 km toabout 9 km.
 8. The method of claim 1, wherein the stocked one or morecoarse granularity fibers are configured to compensate for a fixedamount of dispersion in the optical transmission system corresponding tolengths in a range of about 5 km to about 100 km.
 9. The method of claim1, wherein the stocked one or more fine granularity fibers areconfigured to compensate for a fixed amount of dispersion in the opticaltransmission system corresponding to lengths in a range of about −5 kmto about 5 km.
 10. An inventory of dispersion compensation fibers foruse in an optical transmission system, the inventory comprising: aplurality of coarse granularity fibers, wherein each of the plurality ofcoarse granularity fibers is configured to provide a fixed amount ofdispersion compensation; and a plurality of fine granularity fibers,wherein each of the plurality of fine granularity fibers is configuredto provide a fixed amount of dispersion compensation; whereincombinations of one of the plurality of coarse granularity fibers andone of the plurality of fine granularity fibers span a range of possibledispersion values in the optical transmission system.
 11. The inventoryof claim 10, further comprising: a plurality of memory storage devices.12. The inventory of claim 11, wherein at least one of the plurality ofmemory storage devices is connectable to at least one of the pluralityof coarse granularity fibers, and wherein the at least one of theplurality of memory storage devices is configured to store a uniqueidentifier associated with the at least one of the plurality of coarsegranularity fibers.
 13. The inventory of claim 11, wherein at least oneof the plurality of memory storage devices is connectable to at leastone of the plurality of fine granularity fibers, and wherein the atleast one of the plurality of memory storage devices is configured tostore a unique identifier associated with the at least one of theplurality of fine granularity fibers.
 14. The inventory of claim 10,wherein each of the plurality of coarse granularity fibers is configuredto compensate for a fixed amount of dispersion in the opticaltransmission system corresponding to lengths in a range of about 10 kmto about 100 km.
 15. The inventory of claim 10, wherein each of theplurality of fine granularity fibers is configured to compensate for afixed amount of dispersion in the optical transmission systemcorresponding to lengths in a range of about 1 km to about 9 km.
 16. Theinventory of claim 10, wherein each of the plurality of coarsegranularity fibers is configured to compensate for a fixed amount ofdispersion in the optical transmission system corresponding to lengthsin a range of about 5 km to about 100 km.
 17. The inventory of claim 10,wherein each of the plurality of fine granularity fibers is configuredto compensate for a fixed amount of dispersion in the opticaltransmission system corresponding to lengths in a range of about −5 kmto about 5 km.
 18. The inventory of claim 10, wherein at least one ofthe plurality of coarse granularity fibers is a standard single modefiber and at least one of the plurality of fine granularity fibers is astandard single mode fiber.
 19. The inventory of claim 10, wherein atleast one of the plurality of coarse granularity fibers is a non-zerodispersion shifted fiber and at least one of the plurality of finegranularity fibers is a non-zero dispersion shifted fiber.
 20. Theinventory of claim 10, wherein at least one of the plurality of coarsegranularity fibers is a silica core fiber and at least one of theplurality of fine granularity fibers is a silica core fiber.